UC Irvine

Increasing atmospheric concentrations of greenhouse gases driven by anthropogenic emissions of CO2 and N2O are a critical concern for climate change and global warming. Electrocatalysts which can use renewable energy to directly abate these greenhouse gases via chemical reduction are desirable. This dissertation describes experimental research to develop a new aqueous CO2 reduction electrocatalyst inspired by hydrogenation catalysts, as well as a new organic N2O reduction electrocatalyst inspired by electrochemical CO2 reduction. Lastly, a series of transition metal complexes were chosen and investigated based on their thermodynamic and redox properties to identify metals which activate N2O at milder potentials. Ch. 1 details the translation of [Co(dmpe)2(H)2]+, an aqueous hydrogenation catalyst, into an aqueous electrocatalyst. The hydricity of this compound is pH-dependent in water due to OH binding upon hydride transfer, thus the free energies of CO2 reduction and HER are both thermodynamically favourable at neutral pH. Both HCO2- and H2 are observed under stoichiometric conditions and during controlled potential electrolysis. Ch. 2 establishes [Pt(dmpe)2]2+ as an electrocatalyst for N2O reduction. Controlled potential electrolysis experiments demonstrate good selectivity for N2. Cyclic voltammetry and NMR experiments indicate that [Pt(dmpe)2H]+ and [Pt(dmpe)2OH]+ are key intermediates in the catalytic cycle, and that N2O insertion into the Pt-H is rate limiting. Ch. 3 describes the reactivity of several late transition metal hydrides with N2O. These hydrides span a 15 kcal/mol range in hydride donor strength. While all are demonstrated to react with N2O, there is no apparent correlation between N2O activation and hydride donor strength or pKa.